Field of the Invention
The present invention relates to a technique for focusing on a moving object with an image capturing apparatus.
Description of the Related Art
Conventionally, a technique used in image capturing apparatuses of performing autofocus during continuous shooting to continuously focus on an object (hereinafter, referred to as “servo continuous shooting”) is known.
Japanese Patent Laid-Open No. 2007-206433 discloses, as a technique for performing autofocus during continuous shooting, a method for continuously focusing on an object by repeating scanning using a previous in-focus position as a center. “Scanning” refers to an operation of moving a focus lens in a predetermined range to acquire an evaluation value (hereinafter, referred to as “AF evaluation value”) that is based on the magnitude of a contrast, and searching for an in-focus position. However, in this method, a near-side distance at which a moving object can be focused on is limited. This is because, as the object approaches the image capturing apparatus, even a slight change in the object distance will largely change the in-focus position. In order to bring the limit distance closer to the image capturing apparatus, it is necessary to estimate the scan center position.
In order to solve this problem, Japanese Patent No. 2906238 discloses a method for moving a focus lens, in which information relating to acceleration, on an image plane, of a moving object is calculated, a movement amount, on the image plane, of the moving object is calculated taking into consideration the information, and a defocus amount is corrected based on the movement amount.
However, in the method disclosed in Japanese Patent Laid-Open No. 2007-206433, calculation is performed based on a previous in-focus position of the focus lens that is stored in a storage means, and thus, even when an object is moving at a constant speed, the change in the focus lens position at which the object is in focus is not linear. Accordingly, complex calculation is needed to estimate a focus lens position at which the object is in focus.
Furthermore, in the method disclosed in Japanese patent No. 2906238, since a defocus amount is corrected based on information relating to acceleration on an image plane, it is necessary to calculate the acceleration, and thus the calculation is troublesome. Furthermore, since a change on the image plane is not linear, the calculation thereof is also complex.